A compressor used in a vehicle air conditioner includes a drive shaft and an inner compression mechanism. The compression mechanism is actuated by rotation of the drive shaft. The compressor also includes an electromagnetic clutch to transmit power from the vehicle's engine to the drive shaft. The clutch is engaged and disengaged based, for example, on the cooling load in an external refrigerant circuit. A typical electromagnetic clutch includes a pulley, an armature and a coupling member. The coupling member connects the armature to an inner hub, which is located at the distal end of the drive shaft. The armature is selectively engaged with and disengaged from the pulley. When the clutch is electromagnetically engaged, engine power is transmitted to the drive shaft by a belt, the pulley, the armature, the coupling member and the inner hub. The coupling member, which is supported by the inner hub, separates the armature from the pulley when the electromagnetic force of the clutch is stopped. Rubber dampener (rubber hub) type and a leaf spring type coupling members are known in the art. The leaf springs used in leaf spring type coupling members are practically ineffective as dampeners.
If a coupling member for coupling an armature with an inner hub is made of rubber, torque fluctuation in the compressor is absorbed by the rubber, which serves as a dampener. However, the coupling member must function not only as a dampener but also as a torque transmitting member. Thus, the spring constant of the rubber must be relatively high to make the coupling member durable. The resonance frequency is determined by the moment of inertia of rotation system of the compressor and the spring constant of the rubber. When the spring constant of the rubber is high, the resonance frequency tends to be higher than the lowest frequency of torque fluctuation generated in the rotation system of the compressor. A typical compressor operates at 1000 rpm to 2000 rpm. If the frequency of torque fluctuation of the compressor substantially matches the resonance frequency when the compressor is operating in a normal speed range, resonance occurs and increases the torque fluctuation. The increased torque fluctuation produces noise in the vehicle.
Using leaf springs, in comparison to rubber, to couple the armature and the inner hub increases the resonance frequency. Further, the leaf springs are ineffective as dampeners. Thus, when resonance occurs, torque fluctuation is excessive, which results in seizing and wearing of contact surfaces of the electromagnetic clutch.
An objective of the present invention is to provide a power transmission mechanism that suppresses vibration and noise due to torque fluctuation and prevents the inner parts of the compressor from being damaged.